AUSTIN -- As we approach the fourth anniversary of the Deepwater Horizon oil spill, Margaret Brown takes us back to the Gulf Coast with The Great Invisible, a powerful documentary that reminds those of us who've moved on to other worries that this one is far from finished -- and that a government that proclaimed outrage during the summer of 2010 has seemingly done little to prevent or prepare for another such catastrophe. The film should move those who see it at fests and in arthouses, though it may reach its widest audience on TV, where Brown's last film, The Order of Myths, won a Peabody Award.

The filmmaker, who grew up on the coast of Alabama, spends time there and in other coastal fishing communities, unsentimentally observing poverty among those whose livelihoods have been destroyed. More than once, we hear someone complain that money promised by those administering BP's $20 billion settlement hasn't come or that they got a few checks and then nothing. (Kenneth Feinberg, the attorney in charge of that fund, admits onscreen that he overpromised when it came to timing.) Roosevelt Harris, a volunteer delivering groceries to these families, is our guide through the area, an enjoyable companion who marvels at the poverty endured by his new friends.

While BP predictably refused to participate, the filmmakers secured access to two men who worked on the Deepwater Horizon and the father of another who died there. They have suffered as well, and not just from the considerable emotional damage of seeing close friends perish. Chief Mechanic Doug Brown (unrelated to the director), who earned a six-figure salary on the rig, gets less than a thousand dollars a month as a survivor of the explosion, is in terrible health, and has at least once tried to kill himself; Stephen Stone, a roustabout, relates his experience as a survivor to Somerset Maugham's The Razor's Edge. Both men describe an environment where workers knew safe practices but were increasingly directed by superiors to ignore them. Keith Jones, an attorney who was proud to get his son Gordon a job on the Deepwater Horizon, counts 26 specific cost-cutting measures he believes contributed to the blowout.

Brown has an eye for character, and her film is distinctive in part for its willingness to dwell in the margins instead of cramming in as many eyewitnesses and experts as she can find. In addition to Harris, she tags along with Latham Smith, a colorful tugboat captain who has plenty of opinions about oil. She also, surprisingly, worms her way into a small group of execs from oil companies much smaller than BP, filming them talking casually over drinks and cigars.

Throughout, the filmmaker has an eye on the big picture, one these execs see even if their economic interests color their perspectives. The last section of the film pairs footage of Congressional panels chiding schoolboy-like oil executives with scenes that got less news coverage -- a drilling-rights auction held by the Department of the Interior that earned over $1.7 billion. With that much money to be made, it's no surprise the government quickly lifted the deepwater offshore drilling moratorium, or that more rigs are drilling now than were before 2010. As the film informs viewers that, despite all that scolding in front of cameras, Congress has yet to pass a single new safety law for offshore drilling since the Deepwater Horizon disaster, one can't help but marvel: Here, as with other world-shaking events that could have prompted serious reform, Washington had a moment during which popular sentiment was vehemently pro-reform and failed to do anything about it.